The storage of liquids and gases, the treatment of waste, particularly hazardous waste, the disposal of waste material and monitoring thereof have been the subject of considerable public attention. Although in some matters of public concern, a passive attitude is the norm, the direct relationship between landfill disposal of waste, hazardous waste, the storage of liquids and gas on the one hand and groundwater pollution on the other is particularly critical because of a potential direct link between toxic substances and a person's water faucet. Thus, the public is more active, and even sometimes volatile, in expressing concern in these matters. Groundwater pollution in most instances is not detectable to the human eye and is identified only when the pollution reaches the water tap. By that time, the pollution may be very difficult to correct, and may even require new sources of safe water to be found, involving time, discernible inconvenience and considerable expense.
Most landfill is of domestic origin, but industrial, commercial, and military presence increases the likelihood of hazardous wastes being incorporated in landfill. For example, organic solvents which are used as degreasing agents for cleaning machinery are often detected as contaminants in groundwater.
As another example of contamination of groundwater, leaks from underground storage tanks used primarily for gasoline and other liquid petroleum fuels have had a significant adverse environmental impact in the United States. It has been estimated that there may be as many as 3.5 million underground storage tanks in the U.S. Estimates of the number of those tanks that are leaking tanks are already overwhelming, and the number is expected to continue to increase in the next few years. Many of the groundwater contamination incidents have been attributed to leaking storage tanks.
One of the primary causes of storage tank leakage is corrosion. It will be understood that product loss from the storage tanks by leaking will cause an adverse effect on the environment, endanger lives, reduce income, and require expenditure of millions of dollars in clean-up. A satisfactory system for accurately determining the presence of underground tank leakage is therefore desirable to prevent or reduce the adverse effects thereof.
Various volumetric, non-volumetric, inventory monitoring, and leak-effects monitoring detection methods and systems are known. Certain of these are described in patents which are discussed hereinafter.
Typically, monitoring and detection of groundwater contamination has involved the installation of wells, sample collection, sample preservation and laboratory analysis. These steps are expensive, time consuming, and often subject to error. Further, there is generally a considerable time lag between the identification of a problem and the measured initial results. The monitoring well becomes a permanent environmental change at the study location. Hence, these monitoring and detection methods are not conducive to screening studies in instances where problems are only suspected and many sampling locations are needed. Because groundwater pollution does not generally leave detectable physical evidence on the ground surface, the lack of such easily detectable evidence almost entirely eliminates simple forms of screening to discern potential problems or to further investigate suspected problems.
U.S. Pat. No. 4,709,577 issued Dec. 1, 1987 discloses apparatus and method for detecting leaks from underground gasoline storage tanks and the like. That invention, however, depends on the insertion of a particular tracer into the contents of the storage tank, and the routine or periodic soil samples taken from the soil outside the tank are tested for the presence of that particular tracer. The invention is limited in its application. First of all, it appears inapplicable to general exploration, for it is only practical to insert the particular tracer where an already known facility exists and is suspect. Secondly, knowledge gained from the test results appears restricted to the learning of the simple fact only that a leak has developed in that known facility.
U.S. Pat. No. 2,928,247 discloses a system and method of detecting leakage from an underground storage cavern. Analyzers are provided to sense any stored material which may leak from the underground cavern into an adjacent porous formation. Although this shows the concept of a porous layer being inserted between a leaking source and an analyzer sensor, it appears from this disclosure that the porous formation is relied upon only to slow the rate of leakage to a point to avoid exceeding the capacity of a nearby downhole pump for pumping liquid up to the surface to an analyzer located there.
U.S. Pat. No. 4,618,855 discloses a soil pollution monitoring system which is evacuated to draw air and vapor through sampling tubes that appear to be perforated. Air/vapor samples are contemplated in the operation. Any liquid in the system is considered an abnormality, and special compensation is therefore made for such liquid. The system is complex. Furthermore, it, too, is limited in its applicability.
West German Published Patent Application No. 1,804,441 discloses an underground tank leak detecting system using a pipe with perforated walls in which a second pipe or tube is located to extend along and beneath the tank. This is an oil leak warning system, and air is drawn through the pipe system to carry any oil fumes that might be present to a monitoring unit that in turn establishes the presence of the fumes. This is again limited to a permanent type installation and restricted in its detection ability.
Other known systems also detect volatile hazardous compounds in the environment and are based on instrumental techniques. These techniques may be classified with respect to sensitivity, specificity, and the complexity and sophistication of the instrumentation required. The more specific, sensitive methods often require expensive laboratory facilities, while less sensitive and less specific methods are carried out with relatively unsophisticated field apparatus. Some instruments are not very selective and are capable only of indicating an activity of some kind of volatile compound. Laboratory techniques such as gas chromatography/mass spectrometry may provide a quantification and identification of individual organic compounds from a single sample. Such techniques require the services of trained analysts, expensive instruments and laboratory settings. The least selective instruments include those commonly identified as portable organic vapor analyzers, while more selective laboratory techniques generally are based on chromatography and gas chromatography/mass spectrometry. The portable gas chromatograph is an example of an instrument that is intermediate these extremes.
The several categories of analytical instruments used for the detection of volatile hazardous compounds in the environment require differing techniques for sample introduction. A total analysis, of course, includes the obtaining and introducing of a sample as well as the chemical analysis of that individual sample. Accordingly, an overall analysis may be limited by instrument performance or by limitations imposed by the sample collection and introduction or both.
Instrumental techniques for analysis of organic compounds dissolved in water generally require the collection of a bulk sample of water. Furthermore, access to this water is generally gained by drilling into the subsurface environment and installing a sampling well. Sampling wells generally have an air-to-liquid interface between the well contents and the atmosphere, and dissolved volatile substances may escape from the well water to the atmosphere prior to sampling, potentially producing inaccurate samples. Surface active substances may also migrate to and accumulate at the air-to-liquid interface, producing another potential source of error. Typically, to minimize this problem several well volumes of water are pumped from a sampling well prior to sampling, but this may create turbulence within the well which enhances gas exchange. Moreover, the drawing of a sample from the well to the ground surface then becomes a problem, and specialized submersible pumps that minimize contact between sample and atmosphere in all probability should be added to the system, resulting in a more complex and costly system than desired. Furthermore, wells in and of themselves are costly and often sources of contamination. If the wells are abandoned, they leave the area in a permanent environmental change by their physical presence.
Simply stated, known methods of obtaining samples of groundwater that are representative of the contaminated conditions are not obtained at reasonable costs and without materially disrupting the environment. Furthermore, the known methods do not lend themselves to rapid or short term testing. Nor even do they lend themselves to the most satisfactory long term or permanent testing and observation. Accordingly, it appears desirable to provide a system and method that would overcome these drawbacks. Furthermore, it has been found that the content of water vapor in flue gases may be analyzed for the presence of contaminants, and so preferably the principles of such a method and system should also include the ability to detect contaminants in flue gases.
It has been proposed that for certain purposes it is not necessary to measure the concentration of a particular organic pollutant in the groundwater as such in order to obtain useful information on the general extent and direction of movement of a groundwater contaminant. In particular, it has been proposed that because the soil atmosphere in the zone above the water table, called the vadose zone, also becomes contaminated with volatile organic compounds by diffusion of organic vapors from the underlying water table, measurements may be made of concentrations of organic vapor in the soil atmosphere to delineate the extent of movement of contaminated water. This kind of sampling of the soil zone above the water table would involve minimal or no drilling which with an on-site analytical instrument, would involve handling of gases only. It would appear, therefore, that such sampling would be a cost effective field technique, particularly considering that portable gas chromatographs capable of being hand-carried to an otherwise inaccessible field site are available. This includes the field portable mass spectrometer, and this allows for on-site application of mass spectrometry. The mass spectrometer has the unique potential of being a versatile detector capable of providing a qualitative as well as a quantitative identification of unknown compounds.
In a known trial of this vadose zone sampling, however, too much effort may have been spent on obtaining successful sampling identification with field instruments of the mass spectrometer type. Thus, difficulties with the detector/analyzer segment of the sampling procedure brought an unsuccessful conclusion to the attempt. Moreover, known limitations to vadose zone sampling include the fact that concentrations in underlying groundwaters are not directly measurable by this technique. Such sampling will not reveal the actual degree of contamination of water at a particular depth of concern in an aquifer, and it does not appear suitable for the identification of contaminants which may lie deep within an aquifer. Thus it has appeared that a sampling well or other device is needed to reach the saturation zone itself, involving separate systems for vadose and aquifer testing. The sampling techniques, therefore, preferably should be capable of including subsoil gases, liquids and liquid masses with equal ease and without alteration. Furthermore, sampling to delineate aggression of under surface pollution preferably should include an array of sampling points, which in the previous known systems have been provided by wells.
Such techniques could greatly ameliorate a major problem in the cleanup process of, for example, landfill dump sites, which problem stems from a paucity of information regarding the dump site composition and aerial and volumetric extent. This lack of information has severely impacted all aspects of dealing with dump sites, i.e., remedial investigations and feasibility studies, hazard ranking, risk assessment, site remediation, etc. Performing a general prospecting survey of hazardous fluids including their mobility or stability at a given site is of significant value in developing preliminary overall containment and treatment plans. Thus, a network of relatively low cost implanted soil gas samplers deployed throughout dump site vadose and peripheral zones as well as adjacent aquifers and high permeability strata can be utilized effectively and is desirable for site prospecting. The concept of such an implanted sampler network, however, appears viable only if waste characterization data can be provided quickly and inexpensively and if the sampler can provide samples of all hazardous soil fluids and can interface at the dump site with a variety of analyzer/monitors and secondary samplers.
Accordingly, an urgent need exists for a rapid and relatively inexpensive instrumental method that is capable of obtaining and analyzing samples equally well from soil and from liquids and from an array of positions in either, to determine the existence and extent of undersurface contamination. Desirable characteristics for a solution include something that is relatively portable, easy to operate, and rapid in identification of contaminants.